Device and method for three-dimensional display of images

ABSTRACT

What is disclosed is an image display system comprising an image display device and optical means present at least in front of the viewer, which have a relief structure comprising optical pyramid-shaped elements for suggesting depth in images being viewed by distinguishing between incident light on the left-hand eye and incident light on the right-hand eye of the viewer. Several pyramid-shaped elements are incorporated in the relief structure for each pixel of which the images are built up, as a result of which the alignment of the pixels on the pyramids of the elements will be less critical and, in addition, the occurrence of Moiré distortion in the image is prevented.

The present invention relates to an image display system comprising animage display device and optical means present at least in front of theviewer, which have a relief structure comprising optical pyramid-shapedelements for suggesting depth in images being viewed by distinguishingbetween incident light on the left-hand eye and incident light on theright-hand eye of a viewer.

The present invention furthermore relates to an image display devicesuitable for use in the image display system according to the invention.

Such a system is known from WO 98/17067. The system that is disclosedtherein comprises an image display device or screen which displaysimages which have been position-shifted in succession by imageprocessing means. After being displayed on the screen, said images areconverted by optical means disposed between the screen and the viewer.To that end, the optical means have a relief structure comprisingelements of substantially pyramidic section. As a result of the presenceof the pyramids of the elements, whose apexes are directed towards thescreen, a distinction is produced between incident light on a viewer'sleft-hand eye and incident light on said viewer's right-hand eye. Thisimparts a suggestion of depth in the images perceived by the viewer.

In practice it has become apparent that under certain circumstances thedifferences in clarity between the left-hand eye and the right-hand eyethat are created with the known system are not sufficient for impartinga sufficient perception of depth in the images being viewed.

Accordingly it is an object of the present invention to provide an imagedisplay system for improved display of images comprising depthinformation.

In order to accomplish that objective, the image display systemaccording to the invention is characterized in that severalpyramid-shaped elements are incorporated in the relief structure foreach pixel of which the images are built up.

The advantage of the image display system according to the invention isthe fact that the light output of the images formed by severalpyramid-shaped elements has been increased. Not only does this make theobtained image clearer and easier to view, but it also appears to effectan improvement as regards the perception of depth in the images beingviewed.

In addition to that it is advantageous when using said severalpyramid-shaped elements that the time-consuming, previously necessaryalignment of the pyramids at the position at which each pixel isdisplayed on the image display device is no longer critical as regardsthe obtained light output of the images and the desired depth effect.Thus, a significant saving as regards time and cost price in themanufacture of image display systems according to the invention isobtained.

Another advantage is the fact that only one camera is required at therecording or transmission end in order to effect the required depthperception at the receiving end. Furthermore, the perception of thesuggested depth effect is not restricted to a limited area because thedesired depth effect is substantially independent of the position of theviewer with respect to the image display device.

One embodiment of the image display system according to the invention ischaracterized in that the pyramid-shaped element are arranged in amatrix. As a result, a defined arrangement of rows and columns ofsuccessive pyramids is formed, which can easily be produced by means ofa laser a technique, for example, and which can be inspected forpossible faults in a simple manner, if necessary.

An embodiment of the image display system according to the inventionwhich can be produced in a simple and quick manner is characterized inthat the pyramid-shaped elements comprise four planes.

Another embodiment of the image display system according to theinvention is characterized in that the pyramid-shaped elements each havea base, in which each base of the pyramids of a row takes up oneposition and each base of the pyramids of an adjacent row takes up aposition complementary to said one position. The advantage of thisposition of the bases, which is different for each row, is that it leadsto different perceptions by the left-hand eye and the right-hand eye ofthe active optical surface of one-row in comparison with the other row.This contributes additionally to the difference in the clarity ofperception of one eye in comparison with the other eye. As a result, theperception of depth is enhanced.

One effect which further enhances the perception of depth is thefollowing. It is a well-known fact in physiology that if one eyereceives more light than the other eye, the information relating to saidgreater amount of light will travel more quickly to the brains via thenerves as the amount of light being received increases. This leads to anadditional difference in transit time or phase difference as regardsinformation travelling to the brains, which additional difference intransit time is interpreted by the brains as additional depth in theimage being viewed.

Another embodiment of the image display system according to theinvention is characterized in that adjacent pyramid-shaped elementsexhibit different distances/heights from the apex to the base of thepyramids.

By varying the height of the pyramids over the relief structure, anadditional difference is obtained in that which the two eyes perceive inthe left-hand part and in the right-hand part of the image,respectively. This is in particular of importance with regard to theperception of depth in moving images, in which the movement of the imageis converted into an additional difference between that which isperceived by the left-hand eye and that which is perceived by theright-hand eye, as it were, so that the perception of depth ismaintained.

In connection with said further embodiment it has moreover becomeapparent that the image manipulation technique that may be used willremain simple and easy to implement in software, using commonprocessors.

Another specific embodiment of the invention is characterized in thatthe height of the pyramids increases in one direction whereas saidheight decreases in the opposite direction. The consequence of this isthat movement of the image in a direction comprising a horizontalcomponent, for example, will lead to the desired difference between theamount of light perceived by the left-hand eye and the amount of lightperceived by the right-hand eye. This obtains both with regard tomovement from the left to the right and with regard to movement from theright to the left. In both cases it will result in the desiredperception of depth.

Yet another embodiment of the image display system according to theinvention is characterized in that the direction of a row of thepyramid-shaped elements forming a matrix includes an angle of about 15degrees with the horizontal. With this embodiment of the image displaysystem according to the invention it becomes possible to effect adifference between the amounts of light received by the left-hand eyeand the right-hand eye, respectively, also if a movement in the imagecomprises a vertical component. As a result, depth can be perceived alsoin those cases where the direction of movement comprises a verticalcomponent. Moreover, this embodiment reduces the extent ofMoirédistortion, the well-known effect that occurs when block-shapedpatters are displayed on a television screen, for example, as aconsequence of which moving lines are formed on the screen. The angle of15 degrees has appeared to be an optimum angle in particular whenequilateral pyramids are used and the angles of the base are 60 degrees,therefore, whilst a row begins with a base side which extendsvertically.

One embodiment of the display device that is suitable for use in theimage display system according to the invention is characterized in thatthe optical means, which have a relief structure comprising optical,pyramid-shaped elements, are in the form of a foil, a loose foil, ifdesired, to be applied to the display device, or in that thepyramid-shaped elements are integrated in the front plate of the displaydevice.

Another advantageous embodiment of the image display system is accordingto the invention characterized in that the system comprises means fordisplaying an image built up of frames as well as image manipulationmeans, in which said image manipulation means are arranged for changingthe clarity of frame pixels from the left to the right in one frame andchanging the clarity of frame pixels from the right to the left in theother frame.

To the human eye, the effect achieved by means of theclarity-manipulated frames being displayed in succession is the same asthe effect achieved by using neighbouring pyramids of different height.The image manipulation means, which are to be software-implemented, forman electronic alternative, as it were, for the hardware pyramids.

This embodiment presents an electronic alternative for the opticalembodiment of the system, in which the height of neighbouring pyramidschanges. The exchangeability between optical image processing andelectronic image signal processing as regards the desired difference inlight output between the left-hand eye and the right-hand eye isillustrated by this.

A further alternative embodiment of the image display system ischaracterized in that the system comprises means which make it possibleto control the extent to which the clarity from the left to the rightand vice versa changes.

In this alternative embodiment it is possible to influence the extent towhich a depth effect can be perceived in the images being displayed bycontrolling the degree/gradient of the clarity change.

One embodiment of the image display system which is also quite suitablefor perceiving depth in images being displayed is according to theinvention characterized in that the system comprises a chopper circuitconnected to the display means, which circuit arranges for the frameclarity for pixels from one frame and from the other frame to be turnedoff alternately.

An improved embodiment of the image display system which is suitable fordisplaying stationary images is according to the invention furthercharacterized in that said chopper circuit delivers a signal at afrequency which exhibits a frequency sweep.

One embodiment of the image display device which is suitable for use inthe image display system is according to the invention characterized inthat the optical means having a relief structure comprising opticalpyramid-shaped elements consist of a foil to be arranged on the displaydevice or are integrated in the front plate of the display device. Giventhe fact that, in view of the above explanation, the position of thepyramids on the pixels is no longer critical, said foil may be an easilydetachable foil; when such a foil is not used, the well-known image onthe display device is shown, whereas images imparting a perception ofdepth are shown when a foil which is easy to apply to the image displaydevice is used.

The image display system according to the present invention will now beexplained in more detail with reference to the appended drawing. In thedrawing:

FIG. 1 shows part of the relief structure comprising opticalpyramid-shaped elements for use in the image display system according tothe invention;

FIGS. 2A, 2B and 2C are diagrams and a representation of a pyramid,respectively, which function to explain the system of FIG. 1.

FIG. 1 shows part of the relief structure which may be present on, forexample, a secondary screen or on a display device, hereinafter called ascreen, or be integrated therein. The relief structure may also bepresent on a foil, which may be detachable from the screen, if desired,or on a front plate of such a screen. Examples of a display device are:a screen or monitor, for example for a television, whether or notprovided with a cathode ray tube, an LCD screen or the like. The reliefstructure is made up of optical means in the form of optical,pyramid-shaped elements 1 present in front of the viewer, which havebeen formed in the foil by means of a fine laser technique, for example.The pyramids have a apex T directed away from a viewer who is looking atthe screen. Upon exposure of the screen by a passing luminous spot, thepyramids 1, which are arranged in a matrix formation in FIG. 1, areexposed in succession on the side of their apexes, which light isrefracted by the surfaces of the pyramids 1. In their simplest form, thepyramids 1 of the illustrated pyramid-shaped elements comprise fourplanes, including a base facing towards the viewer. The luminous spotforms a pixel on a picture line in a manner which is known per se, andseveral such lines form an image. In those cases in which an imageconsists of two “interlaced” frames or fields, the frames are written tothe screen as half-images. A pixel is made up of two pixels in thatcase, one from a so-called uneven frame and one from an even frame. Theprecise alignment of the various pixels on the relief comprisingpyramids 1, in a manner in which the left-hand eye and the right-handeye receive different amounts of light from the pixels, so that theviewer can perceive depth in the image on the screen, is problematic.The way in which depth can be suggested in this way is schematicallyindicated in FIG. 1, in which the hatched parts in the upper twopyramids 1 indicate the amount of light which the left-hand eye, giventhe position of the pyramids on the left-hand side, receives from therelief structure, whilst the hatched parts in the lower two pyramids 1indicate the amount of light which the right-hand eye receives from therelief structure from the same left-hand side. The differences in lightor clarity with which the two eyes have to cope and the associateddifferences between the time of arrival of said clarity information atthe brains and the time of interpretation thereof impart the perceptionof depth in the image being viewed.

Inaccurate alignment of the relief on the pixels will lead to a poorperception of depth, however, and to the well-known Moiré distortion inthe image being viewed. The two problems can be solved at once byincorporating several pyramid-shaped elements 1 in the relief structurefor each pixel of which the images are built up. In this connection itmay be considered to use a number of pyramids which ranges between 3×3pyramids and (preferably) 9×9 or more pyramids per pixel, for example.Suitable techniques for realising the pyramids include: a lasertechnique, x-ray lithography, an I beam technique, or the mechanicalsuper high precision diamond cutting, which currently is capable ofrealising up to 0.2 μm.

As FIG. 1 furthermore shows, each base of the pyramid-shaped elements ofthe same—first—row extending to the right-hand bottom corner or to theright-hand upper corner takes up one position, in which the right handtip of the base points to the right in all cases. Likewise, each base ofan adjacent—second—row extending to the right hand bottom corner or tothe right-hand upper corner takes up a position complementary to saidone position, in which the left-hand tip of the base points to the left.In this way a honeycomb structure of bases is formed, as it were, whichleads to the differences in clarity on which the perception of depth isbased.

If a perception of depth is to be maintained in the case of movingimages on the screen as well, the movement must be converted intodifferences in clarity between the left-hand eye and the right hand eye,as it were, in order to create the perception of depth in this manner.This idea is embodied in a possible embodiment in which the successivepyramids 1 exhibit different distances/heights, measured from the apex Tto the base G of the pyramids. In particular, the height of the pyramids1 increases from the left to the right in FIG. 1, for example, whilstthe height of the adjacent row of pyramids 1 decreases from the right toleft. The gradual difference in height increases from 0 to 10 μm, forexample, for one row of pyramids and decreases from 10 to 0 μm for theadjacent row. If, for example, a vertical line portion of the imageshifts in horizontal direction in that case, the differences in clarityresulting from the differences in height of the pyramids 1 will impart aperception of depth.

In order to achieve differences in clarity and perception of depth alsoin the case of the direction of movement comprising a verticalcomponent, the relief structure as shown in FIG. 1 is turned. Inpractice the optimum angle of turning is connected with the magnitude ofthe angles forming the base G of the pyramids 1. For the equilateralbase comprising angles of 60 degrees, the direction of the row of thepyramid-shaped elements forming a matrix must extend at an angle ofabout 15 degrees to the horizontal, so that also vertical movements willimpart perception of depth and the Moiré effect will be furthersuppressed. Thus, also movement of an object in the image from the rearto the front or vice versa can still be perceived as a realisticmovement towards or away from the viewer.

Image displays systems which are known per se, such as televisionsystems, are arranged for displaying images which, as mentioned above,are built up of even and uneven frames. Furthermore, the system may befitted with image manipulation means which are arranged for changing theclarity of frame pixels from the left to the right in one frame andwhich are likewise arranged for changing the clarity of frame pixelsfrom the right to the left in the other frame. It will be understoodthat it is possible to adjust the degree of depth to be displayed byinfluencing the gradients of the clarity lines of FIGS. 2A and 2B, whichis indicated by means of arrows. In practice the image displays systemwill comprise similar means for controlling the degree in which theclarity changes from the left to the right and vice versa. Reversal ofthe gradients of the clarity lines even makes it possible to display theimage slightly in front of the screen, in which it seems as if theobjects being shown emerge in part from the screen.

So far, it was movement in the image which led to a perception of depth.In order to further improve the perception of depth in the case ofmoving images, said perception can also be suggested by electronicmeans. This is done by incorporating a chopper circuit, which isconnected to the display means, in the image display system, whichchopper circuit arranges for the frame clarity for pixels from one frameand from the other frame being turned off alternately. This is shownmore clearly in FIGS. 2A, 2B and 2C. In this case it obtains for theuneven frame that pixels present on the left on an uneven line will bedisplayed darker than pixels present on the right on the uneven line(see FIG. 2A). Conversely it obtains that pixels present on the right onthe even lines will be displayed darker than pixels present on the lefton the even lines (see FIG. 2B). This aspect makes it possible tocontribute electronically rather than optically to the perception ofdepth, and also in this case a time difference is created between thereception of light by the left-hand eye and the right-hand eye. FIG. 2Cschematically shows how a matrix of pyramids 1 initially only receiveslight from the pixel of the even frame which, after refraction, issupplied to one of the eyes. Shortly afterwards, the other eye receivesthe pixel from the uneven frame. The corresponding pixels have adifferent light intensity for the left-hand eye and the right-hand eye,however, thus enhancing the suggestion of depth perception in the imagesbeing displayed.

In the case of computer monitors, for example, the chopper frequency maybe 10 MHz, depending on the number of pixels of the image. In particularin the case of stationary images, the perception of depth can beenhanced by having the chopper output signal exhibit a frequency sweep,which may be around 1 MHz in that case. The chopper signal having avarying frequency will produce an additional change in clarity in thatcase, which in turn will lead to an additional depth effect, inparticular for stationary images.

The foregoing obtains both for “interlaced” image display, in which evenand uneven frames are displayed in succession, and for “non-interlaced”image display. In the latter case the succession of frames is asuccession of full frames rather than a succession of even and unevenframes, as was the case in the preceding explanation. The image displaysystem can also be used on monitors and on game computers.

1. An image display system comprising an image display device andoptical means present at least in front of the viewer, which have arelief structure comprising optical pyramid-shaped elements forsuggesting depth in images being viewed by distinguishing betweenincident light on the left-hand eye and incident light on the right-handeye of viewer, characterized in that several pyramid-shaped elements areincorporated in the relief structure for each pixel of which the imagesare built up.
 2. An image display system according to claim 1,characterized in that the pyramid-shaped element are arranged in amatrix.
 3. An image display system according to claim 1, characterizedin that the pyramid-shaped elements comprise four plans.
 4. An imagedisplay system according to claim 1, characterized in that thepyramid-shaped elements each have a base, in which each base of thepyramids of a row takes up one position and each base of the pyramids ofan adjacent row takes up a position complementary to said one position.5. An image display system according to claim 1, characterized in thatadjacent pyramid-shaped elements exhibit different distances/heightsfrom the apex to the base of the pyramids.
 6. An image display systemaccording to claim 5, characterized in that the height of the pyramidsincreases in one direction whereas said height decreases in the oppositedirection.
 7. An image display system according to claim 1,characterized in that the direction of a row of the pyramid-shapedelements forming a matrix includes an angle of about 15 degrees with thehorizontal.
 8. An image display system according to claim 1,characterized in that the system comprises means for displaying an imagebuilt up of frames as well as image manipulation means, in which saidimage manipulation means are arranged for changing the clarity of framepixels from the left to the right in one frame and changing the clarityof frame pixels from the right to the left in the other frame.
 9. Animage display system according to claim 8, characterized in that thesystem comprises means which make it possible to control the extent towhich the clarity from the left to the right and vice versa changes. 10.An image display system according to claim 8, characterized in that thesystem comprises a chopper circuit connected to the display means, whichcircuit arranges for the frame clarity for pixels from one frame andfrom the other frame to be turned off alternately.
 11. An image displaysystem according to claim 10, characterized in that said chopper circuitdelivers a signal at a frequency which exhibits a frequency sweep. 12.An image display device suitable for use in the image display systemaccording to claim 1, characterized in that the optical means, whichhave a relief structure comprising optical, pyramid-shaped elements arein the form of a foil to be applied to the display device, or in thatsaid optical means are integrated in the front plate of the displaydevice.